Precipitation of NaHCO3 and NH4Cl as described above is, in its basic principle, known as the Solvay soda process, which has been industrially dominating for a long time. Further we refer to U.S. Pat. No. 6,180,012 describing a closed tank in which enters CO2-rich exhaust and seawater (with NaCl) and in which separately ammonia NH3 is injected, and fresh water is formed. Sodium hydrogen carbonate NaHCO3 and ammonium chloride NH4Cl precipitate to the bottom and are separated from seawater, which is transformed to fresh water.
It may be inefficient not to mix salt water and ammonia NH3 before the injection into the chamber, as the process described in U.S. Pat. No. 6,180,012, because the components NH3 and NaCl may not have sufficient time to be effectively mixed before further reaction with CO2 in the exhaust gas. Further, it is a disadvantage of the U.S. Pat. No. 6,180,012 that the injection takes place only in a limited upper portion of the tank, and not a more thorough mixing, e.g. in a more extensive portion of the tank. It is a further disadvantage of the U.S. Pat. No. 6,180,012 that the process takes place with inlet of an exhaust gas to a closed tank, because the closed tank will form a counter pressure against the outlet from the gas turbine, and thus there is a risk of a considerable reduction of the gas turbine efficiency.
A typical gas turbine of 25 Megawatt (MW) generates an exhaust flow of about 3.3 kg/s of CO2. That represents a large and undesirable production of CO2 considering the probable contributions to greenhouse effects on the global atmosphere. Further, we expect that the unified process according to the invention also will prove commercially healthy because several countries may incur official CO2-fees and/or trade CO2 emission permissions, so-called “green certificates”.
The process according to a preferred embodiment of the invention has its greatest potential in those parts of the world in which there is a lack of fresh water, e.g. in the Middle East, Western Africa, The Read Sea, etc. One of the main purposes of the invention is to contribute to the use of liquefied natural gas (LNG), seawater and ammonia for an electricity production of significantly reduced CO2-emission, and evaporation of LNG simultaneously with soda production and fresh water production, in which all the products have a sales value. Considering that the invention also improves the efficiency of the electricity production from the gas turbine, by cooling the air to the gas turbine by means of LNG, the invention represents an essential improvement for efficient use of the Solvay process. Further, the process is dependent of low sea water temperature in order to achieve efficient removal of CO2, about 10° C. There is a potential incompatibility in the facts that the seawater temperatures rarely are low in those coastal areas of the world in which there is a lack of fresh water for agricultural purposes or alternatively industrial purposes. Further, there is a potential incompatibility in the facts that evaporation of LNG requires a high seawater temperature, whereas the removal of CO2 requires a low seawater temperature. The preferred embodiment of the present invention aims at combining these seemingly counteractive effects, thereby creating an improved process that should be commercially applicable and having a large market potential, particularly in those areas mentioned above.
An article called “Chemical Separation Process for Highly Saline Water, 1. Parametric Experimental Investigation” in Ind. Eng. Chem. Res., 1996, 35, 799-804, describes the separation of highly saline waters under various conditions and is carried out using a partial-desalting process. The method utilizes a series of chemical reactions involving conversion of Sodium Chloride, the major constituent in saline waters, into sodium bicarbonate, which precipitates under the experimental conditions, and ammonium chloride, which can be separated by crystallization. Experiments of absorption of carbon dioxide in an ammoniated brine have demonstrated the efficiency of the method.